1. Field of the Invention
The present invention relates to an endoscope comprising a fluid-pressure actuator which can extend or contract in response to the supply or discharge of a fluid.
2. Description of the Related Art
U.S. Pat. No. 4,794,912 discloses an endoscope which employs a fluid-pressure actuator to forcibly bend the bendable portion of the insertion section thereof. The fluid-pressure actuator is comprised of an elastic tube, and a flexible mesh tube fitted around the elastic tube and made by inextensible filaments. When a fluid is supplied into the elastic tube of the actuator, the tube expands in the radial direction thereof, and thus contracts in the longitudinal direction thereof (in short, the tube shortens). As a result, a bendable portion-operating wire is pulled, and the bendable portion is bent or curved, accordingly.
The above fluid-pressure actuator greatly expands in the radial direction when its elastic tube is supplied with a fluid to operate the bendable portion. To incorporate the actuator in the insertion section, therefore, it is necessary to determine the actuator's installation space in consideration of the maximum diameter of the actuator.
When the hydraulic-pressure actuator expands in response to the supply of a fluid into the elastic tube, it may happen that the actuator will touch or strongly press some other structural component arranged inside the insertion section. This problem can be solved by employing a cover or the like, but the size of such a cover has to be determined in consideration of the maximum diameter of the actuator, and the actuator's installation space has to be widened, accordingly. Since the size of the insertion section is determined by the diameter of the portion in which the actuator and cover are contained the insertion section is inevitably large.
The fluid-pressure actuator can be used for operating a mirror by which to change the vision field of the objective optical system of the endoscope. In this case as well, the insertion section of the endoscope is inevitably large.